Doctors often talk about weight loss in terms of numbers on a scale, but a new study shows that what you lose matters just as much as how much you lose.
Researchers at Vanderbilt Health found that both weight loss surgery and new medications like semaglutide and tirzepatide help people with obesity lose fat and improve their overall body composition.
Body composition is the mix of fat and fat-free mass in the body. Fat mass (FM) includes body fat, while fat-free mass (FFM) includes lean muscle, bones, water, and other parts of the body that are not fat.
Having too much fat mass is linked to a higher risk of diseases like heart disease, diabetes, and even early death. But having more fat-free mass, especially muscle, can protect you from these risks.
In this study, the researchers looked at the health records of more than 3,000 people between the ages of 18 and 65. Some had undergone weight loss surgery between 2017 and 2022. Others were treated with weight loss drugs between 2018 and 2023.
These drugs, known as GLP-1 receptor agonists, include semaglutide and tirzepatide, which are commonly used to help people lose weight and manage type 2 diabetes.
The study left out people who had serious heart or kidney problems, since those conditions could affect the results. The researchers used a method called bioelectrical impedance analysis to measure changes in body composition.
This tool estimates how much of the body is fat and how much is fat-free, based on factors like age, weight, height, gender, and other medical history.
The results were promising. Over a 24-month period, both types of treatment—surgery and medication—helped people lose a large amount of fat mass and a smaller amount of fat-free mass.
Importantly, the ratio of fat-free mass to fat mass went up, which means their body composition improved. This is a good sign because it shows people were losing mostly fat while holding on to more of their muscle and other lean tissues.
The study also found that men tended to keep more of their fat-free mass than women after losing weight, especially in the long term. This suggests that male patients may find it easier to maintain their muscle while losing fat.
The researchers say more studies are needed to understand why this difference exists and how to help everyone maintain muscle during weight loss.
The researchers concluded that both medical and surgical treatments for obesity are effective in improving body composition, not just weight. This is an important reminder that losing fat—not just weight—is key to better health.
The study was published in the journal JAMA Network Open. It adds to the growing body of evidence that newer weight loss drugs and bariatric surgery can both be powerful tools in the fight against obesity, especially when used with proper medical guidance and long-term support.
If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight.
For more health information, please see recent studies about a simple path to weight loss, and results showing a non-invasive treatment for obesity and diabetes.
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